Among the acts who had been scheduled to perform included the Foo Fighters, Eminem, The Offspring, Good Charlotte and 30 Seconds to Mars, whose frontman, Jared Leto, expressed his condolences yesterday on the band's website.

"Our deepest thoughts and sympathies to the families and friends of those who lost their lives today at the show in Belgium," he wrote. "We are absolutely devastated that this celebration ended in tragedy. To those that were injured we are sending thoughts and prayers. Obviously under these horrible and dangerous circumstances, and out of respect for those who have passed, Thirty Seconds to Mars will not be playing. We love you all and hope tomorrow brings a better day."

Meanwhile, other artists have taken to Twitter to pay their respects as well.

Benji Madden of Good Charlotte tweeted, "Sad day here at Pukkelpop. One of our favorite festivals to play. Sad this happened today. Hearts are with the victims here today," as the Foo Fighters wrote: "Our hearts go out to everyone affected by the tragic events at Pukkelpop."

Sadly, of course, this all comes on the heels of the other concert-related tragedy at the Indiana State Fair last weekend.

Sugarland, who had been waiting to take the stage that fateful day as high winds blew scaffolding down onto the front rows and killing five people, called for a moment of silence on Thursday night at the start of the band's show at the Hard Rock Pavilion in Albuquerque.

The group's Jennifer Nettles followed up by telling the audience that they were going to "try our best to put on our professional faces and come out here for you and celebrate the joy and the healing power of music."